GtkTreeIter internals (was RE: signals versus vfuncs)

[Murray Cumming Comneon com]

> > > Iterators usually contain pointers to internal data structures, 
> > > Paths are just an ordinal representation of a (potential) node 
> > > position. Prepare to accept zero'd iterators (I sometimes 
> get some 
> > > from GtkTreeView after changing between models).
> 
> [...]
> 
> > is there any way at all to get notification when an iter is 
> no longer 
> > in use? perhaps there's something simple i'm missing...
> 
> there's no way to know when an iterator is being freed or 
> copied since they are pure value objects. but that's not a 
> real problem, because an iterator basically "refers to a 
> certain state of a model", rather than maintains its own 
> state (which would require notification/hooks).
> 
> if you implement your own model and need to deal with 
> life-time issues and iterators, you basically do:
> 
> setup_model() {
>   model->stamp = 1;
>   model->glue_object = new_glue_object();
> }
> 
> modify_model() {
>   model->stamp++; /* "invalidates" all iterators with old stamp */
>   destroy_glue_object (model->glue_object);
>   model->glue_object = new_glue_object();
> }
> 
> fill_iter() {
>   iter->stamp = model->stamp;
>   iter->data1 = model->glue_object; /* valid as long as stamp 
> is valid */
>   iter->data2 = ...;                /* valid as long as data1 
> is valid */
> }
> 
> use_iter() {
>   g_return_if_fail (iter->stamp == model->stamp);
>   /* since iter->stamp is valid, iter->data1 is also valid */
>   use_glue_object (iter->data1, iter->data2);
> }

This is a very useful email. Thanks.

I just implemented a custom TreeModel in gtkmm:
http://cvs.gnome.org/bonsai/cvsblame.cgi?file=gtkmm%2Fexamples%2Ftreemodelcu
stom/exampletreemodel.cc&rev=&root=/cvs/gnome

At the moment I'm just mashing a row-number integer into
GtkTreeIter::user_data, as you can see on line 255 there. Obviously I need
to store some more complex data to represent a full potential path in a
model with children.

I don't think I've understood how I would use this glue_object idea to do
that. I suppose this glue_object could map GtkTreeIters to my "potential
path" data, but how would I release (or update) the old invalid glue_object
after creating a new one or updating it, when I mark all old GtkTreeIters as
invalid?

Murray Cumming
www.murrayc.com
murrayc usa net